CRYSTAL VISCOPLASTIC MODELING OF FILM COOLING HOLES IN SINGLE CRYSTAL NICKEL-BASED SUPERALLOYS

Abstract In the advancement of gas turbine technology, increasing thermal efficiency is a primary objective, and one of the most effective methods to achieve this is through elevating the turbine inlet temperature (TIT). Higher TIT enhances the specific power output by enabling greater energy extraction from combustion gases. In the initial turbine stages, blades are exposed to TITs of approximately 1500°C, which significantly exceed the thermal limits of most structural materials. Effective cooling strategies are crucial to mitigate blade surface temperatures. Among various techniques, film cooling will be the focus of this study. Coolant is introduced through discrete holes located at the leading and trailing edges of the turbine blade, forming a protective film. However, the presence of film cooling holes negatively impacts the structural integrity and service life of turbine blades. Nickel-base superalloys (NBSAs) have been widely employed in gas turbine components, such as turbine blades, due to their superior mechanical and thermal properties, such as higher strength and resistance to creep and cyclic fatigue. The inclusion of film cooling holes leads to stress concentrations and plastic stress localization, influenced by thermomechanical loading and anisotropic properties of Single Crystal (SX) and Directionally Solidified (DS) NBSAs. These factors lead to fatigue crack initiation around densely placed cooling holes. This study utilizes crystal viscoplastic (CVP) material models for a generic SX NBSA. Finite element analysis is carried out at various temperatures and material orientations. Specimen geometries include a thin plate and one with densely arranged holes.